Equipments of this type, commercially known as double cutters, are used in systems for the automatic processing of documents previously printed on the continuous forms.
The double cutters can operate “on-line”, downstream from slitting equipments, known as “merger” which divide the basic forms in longitudinal sense, or can operate “off-line” on, already separated, independent forms.
The double cutters of known type cause the forms to advance contemporarily or in alternate way and provide to separate, by means of a single blade, the printed sheets, single or overlapped, for the forming of the documents and the following processing. Moreover, the cutters can trim the edges of the separated forms when the form of origin is provided of lateral feed holes or for reduce the width of the form. For reason of cost and operative flexibility, cutting devices are used having blades with movement of alternative type, for instance guillotine like, and therefore providing the arrest of the form in association with the cutting.
In the case of use of a double cutter, on-line with the slitting equipments, the forms emerging from the merger have the same velocity which is substantially constant, while the forms entering the cutter have varying instantaneous velocity, associated to the intermittent motion of the form internally to the cutter. For compensating the differences of velocity, the portions of the forms between cutter and merger have a length greater than the distance between cutter and merger, so as to form two extended loops.
The operational speed of the commercial cutters is conditioned by the velocity of the cutting device and the stresses to which the entering forms are subjected. Particularly good results have been obtained with the cutting equipment described in the Patent Italian N. 1.360.399 [EP 1 741 653], assigned to Tecnau S.r.l. This equipment provides additional loops of reduced length, upstream of the cutting device and uniformed velocity of the forms at the input of the equipment. It allows reaching the limit determined by the cutting device for the separation of overlapped sheets. Nevertheless, the overall productivity is less of that theoretical, when one of the forms should be arrested for the production of documents having an odd number of sheets or for a particular arrangement of the documents in the unseparated form. Moreover, the differentiated motion of the forms, after the longitudinal separation, renders more difficult to make uniform the velocity of the forms at the input of the equipment.
U.S. Pat. No. 6,341,773, also assigned to Tecnau S.r.l., discloses a dynamic sequencer for sheets of printed paper including a cutting equipment. The documents are printed according to a predetermined order with pages arranged in a flanking relationship, while the sequencer provides to overlap the separated sheets on a collecting station. The various sheets are separated by a transversal and longitudinal cutting equipment which operates on the full width of the form, while two extractors extract the separated sheets from the cutting equipment. For documents including pages arranged on flanked sheets, both the extractors are actuated for the simultaneous extraction and movement of the sheets. For flanked sheets belonging to different documents only one of the extractors is actuated for the advancing of the respective sheet and completing the first document. The other sheet of the second document is extracted by the other extractor upon the releasing of the first document. Therefore, also this cutting equipment should be arrested for the production of documents having an odd number of sheets or for particular arrangements of the documents. Further, the cutting equipment and the associated sequencer are cumbersome in view of used transport belts, which extend longitudinally and have components divergent in height and components converging in height and toward the longitudinal axis.